Add type inference for super method invocations.

pkg/front_end/testcases/inference/super_method_invocation.dart.dartk.expect

+library test;
+import self as self;
+import "dart:core" as core;
+
+class C extends core::Object {
+  constructor •() → void
+    : super core::Object::•()
+    ;
+  method f() → core::int
+    return 0;
+}
+class D extends self::C {
+  constructor •() → void
+    : super self::C::•()
+    ;
+  method g() → void {
+    dynamic x = super.f();
+  }
+}
+static method main() → dynamic {}